Process of production of lead solutions from lead ore.



s. w. ANDERSON & a; 0. KAAR. PROCESS OF PRODUCTION '0]? LEAD SOLUTIONSFROM LEAD ORE.

APPLICATION @ILED DBO. 2'2, 1912. 1,083,910. I Patented Jan. 13, 1914.

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SAMUEL W. ANDERSON AND GROVER C. Kit-AR, 0F SPUKANLE, lJVASHTHGlTUIQ".

PROCESS Oli' PRODUCTION OF LEAD SOLUTIONS FROM LEAD (THE.

To all whom it may concern.

Be it known that we, SAMUEL W. Arman sort and GROVE C. KAAR, citizens ofthe United States, residing at Spokane, in the county of Spokane, Stateof Washington, have invented certain new and useful Improvements inProcesses of Production of Lead Solutions from Lead Ore, of which thefollowing is a specification.

This invention relates to a novel process and apparatus for themanufacture of lead solutions directly from lead ore (galena) by a wetprocess and without the usual smelting of the ore to metallic lead; andit comprises a process first of obtaining the lead in the form of a leadnitrate solution, and then of purifying this solution from accompanyingimpurities; and it also comprises a novel apparatus for effecting suchsolution; all as more fully hereinafter set forth and as claimed.

The objects of the invention are the production of pure solutions oflead and particularly of pure lead nitrate solutions directly from leadsulfid ore in an eflicient and economical manner. I

Briefly the process of dissolving the ore comprises pulve'rizing the:ore, treating the pulverized ore with a 7% solution of nitric acid at atemperature of 150 to 165 T recovering the oxids of nitrogen in the formof dilute nitric acid, mixingt-his dilute nitric acid wit-h concentratedacid to give the standard solution for dissolving the lead andpurifyingthe impure lead nitrate solution from impurities, andparticularly from iron, by precipitating the iron in two successivestages, as more fully hereinafter described. The accompanying drawingsillustrate the apparatus in which this process can be carried out.

Figure 1 is an elevational view of our improved apparatus. Fig. 2 is adetail view showing in section one of the reaction ves-' sels andillustrating the stirrer used therein. Fig. 3 is a side elevation of oneof the vessels such as is shown in Fig. 2 with certain of the connectionpipes shown in sections.

Concentrated nitric acid is produced from sulfuric acid and sodiumnitrate (in a still not shown). This concentrated acid is diluted withthe dilute acid from the tower E to form the standard 7% solution. Thesolution of lead sultid is ef ected in the stone ware vessels G whichare of anon-porous Specification of Letters JEatent.

Application filed December 2'7, 1912.

Serial No. @8339.

character and which are provided with an agitator c and with stopperedopenings Z for charging the acid and ore. The ore pulverized to suitablemesh (-10 to is charged together with sufiicicnt of the '2'% acid intothe vessels C, enough acid being used to dissolve all or most all of thelead sulfid. The jars C are provided with outlets d connected with thepipe 6 leading through the pipe l) to the bottom of the regeneratingtower E. The vessels Q are set in a tank M filled with water andprovided with steam -coils N for heating the water and the vessels to atemperature of to F. At this temperature solution of the ore is effectedwith accompanying agitation and a solution of lead nitrate obtained. Inpractice it is found that all of the acid does not combine with the leadand that the resuiting solution of lead nitrate contains more or lessacid. The neutralization of this acid will be referred to below. It isfound also that the hydrogen sulfid formed by the ac 'tion of the nitricacid and lead sulfid at this elevated temperature decomposes part of thenitric acid into oxide ofnitrogcn, and that about 25% of all the acidcharged is thus converted. Means is provided according to .the presentinvention for recovering these gases as dilutenitric acid and for usingthem again in the process. After the reaction has been completed at theconstant temperatures indicated there has heen formed nitrate of leadnitrate of iron from the iron ore accompanyingthe lead, sulfur and theonids of nitrogen. The oxide of nitrogen, however, escape as gases. andare recovered in the tower E. There remains in the vessels Ganyundecomposed galena at the bottom of the vessels, and also a layer ofthe silicious por t-ion of the ore above the galena; and the solution oflead nitrate thereahove, with some of the sulfur at the bottom and mostof it at the top of this solution in the form of a scum. The stonewarefaucets at the bottom of the jars are now opened and the solution of thenitrates withdrawn into the trough F leading to the settling tanlr G.The galena is so heavy that most of it does not flow out but remains inthe jars C; while the silicious material, sulfur and nitrate solutionflow to the settling tank, The excess of ore remainsv in the jar andwill be acted upon in. the subsequent reaction. it will thus be seenthat by means of the steam Patented J '13:,

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Tilt) to the desired extent. It is then mixed with i the concentratedacid to form the standard 7% solution; It will thus be seen that theacid which would otherwise be lost is returned to the reaction and usedagain with resulting economy and with resultingdecrease in the necessaryamount of concentrated acid. Moreover, the concentrated acid is thusdiluted without the use of water itself.

The specific structure of the inside of the tower E may vary, and thetower may be filled with balls, plates or other baffles. It has beenfound that the tower described in British Patent 14,774 of 1896 givesexcellent results. In this tower the intimate mixture of the oxids ofnitrogen with the air and steamand oxidation thereof is effected, andabsorption of the nitric acid formed also takes place with the water ordilute nitric acid flowing down through the tower.

The reactions taking place in the dissolv- -ing of lead sulfid by nitricacid are as follows, it being understood that more or less iron, usuallyas iron sulfid, is present with the lead ore and is dissolved at thesame time. a

Lead.

Lead is thus changed from lead sulfid to lead nitrate, hydrogen sulfidbeing formed which reacts with a further amount of nitric acid to formsulfur and oxids of nitrogen. Similarly the iron sulfid (pyrites) isdissolved as ferrous nitrate, hydrogen sulfid and sulfur being set freeand reacting the same as already described. Silicious matter is notaffected. Any silver originally present as chlorid or sulfid remainsunaffected in the residue. If, however, it is present in such form as togo into solution as silver nitrate, it is precipitated as chlorid ofsilver by a small amount of a solution of common salt, at thistemperature and dilution the lead not being precipitated as chlorid.

The lead nitrate solutions are separated from the sulfur and sediment inthe settling tank G and are-then run into the tank H where any silver isprecipitated as silver chlorid by a solution of sodium chlorid. Thesolution then flows into the tank K where the subsequent purification iseffected. This solution now contains, besides the lead.

nitrate, principally the iron dissolved as ferrous nitrate, a part ofwhich however may be present, due to oxidation, as ferric nitrate. Smallamounts of arsenic and bismuth may also be present as impurities. It. isdesired to obtain the lead in the form of a pure solution free fromthese impurities. To effect this result there is added to the solutionin the tank K at a boiling temperature obtained preferably by the directinjection of steam and air (by means not shown), an alkali which owingto its cheapness is advantageously sodium carbonate or soda ash, eitheras a solid or as a concentrated solution. Suflicient soda is added toneutralize any acid present and enough in excess to precipitate the ironaccording to the following reactions.

For ferric iron.

II. Fe (CO -{-3H O 2Fe(OH) +3CO or I and 11- For ferrous iron. III.FetNO +Na C0 FeCO +QNaNO IV. lTeCQ +3H O+O:QFe(OH) +2CO For lead. V. Pb(N0 {Na CO :PbCO }2l laN() From these reactions it will be seen that theiron is first precipitated as carbonate but is at once decomposed intohydroxid'and carbonic acid. The ferrous nitrate will be thrown down asferrous carbonate, but will be oxidized in the hot solution by the steamand air and will be converted to ferric hydroxid. The iron is thusconverted into an insoluble precipitate. The action, however, is notselective with respect to the iron and to the exclusion of the lead.More or less of the lead will also be precipitated as carbonate butowing to the relative solubilities of the lead carbonate and the ironcarbonate the lead will be again dissolved and iron carbonate, or ratherhydroxid, formed so long as there remains iron nitrate in the solution.Accordingly, and in order to prevent loss of lead, only sufficient sodais added at first iuoeaaio I to precipitate most but not all of theiron. When the reaction is complete an equilib rium will be establishedand the lead will still remain in solution with a small amount of theiron. There is then added a small amount only of the alkali to throwdown the remaining small amount of iron. By

proceeding in this manner the lasttraces of iron can be removed withoutloss of any appreciable amount of lead. In practising this precipitationand purification operation the iron content is determined from previousanalysis and the quantity of soda added is such as is known to be lessthan the amount required to precipitate all of the iron as ferrichydroxid. After adding the soda the solution is heated in an open tankby the injection of steam and the iron thus precipitated as the ferrichydroxid, either directly or first as the ferrous compound followed byoxidation. Any lead precipitated as carbonate reacts with the ferriciron in solution to precipitate the latter, the lead going again intosolution as already described. Thus all the iron corresponding to theamount of alkali added is precipitated without accompanyingprecipitation of lead at the end of the reaction. The precipitation isnow repeated adding only a slight amount of soda. Any slight amount oflead precipitated during this last step can be left in the tank to bedissolved by the next charge of acid lead nitrate solution.

Instead of using sodium carbonate, sodium hydroxid or mixtures of sodiumhydroxid and carbonate, or of other alkalis such as potassium hydroxidor carbonate can be used. When sodium hydroxid is used the precipitationtakes place according to the following equation.

ferrous hydroxid and subsequently oxidized to the ferric form. Any leadhydroxid formed interacts with the ferric nitrate as already describedwith respect to the lead carbonate. The reaction thus proceeds in ananalogous manner whether the carbonate or hydroxid'of the alkali isused.

Traces of arsenic and bismuth present in solution will be removed uponaddition of the alkali, the arsenic combining with the ferric hydronidto form basic ferric arsenite, and the bismuth being hydrolized to theinsoluble sub-nitrate.

After removal of the iron and other inipurities. the lead nitratesolution is sufficiently pure so that it can be treated at once withprecipitating agents in the tank L and the lead obtained either asbasic. carbonate by precipitation with a mixture of sodium hydroxid andsodium carbonate, or as lead chromate by precipitation with an alkalichromate. The novel precipitation method for effecting thisprecipitation, and the recovery and reuse of the various solutionstherefrom, are described and claimed in an other application.

We claim 1. The process of purifying lead nitrate solutions fromaccompanying iron nitrate which'comprises adding to such solutions anamount of an alkali insufficient to precipitate all of the iron asferric hydroxid, heat' ing such solution to eii'ect reaction bet 'eenany precipitated basic lead compounds and the remaining iron in solutionto form the insoluble iron precipitate and the soluble lead compound,and finally adding sutlicient alkali to precipitate the remaining smallamount of iron as ferric hydroxid.

2. The process of purifying lead nitrate solutions from accompanyingiron nitrate. which comprises adding to such solutions an amount ofsodium carbonate insuilicient to precipitate all of the iron as ferrichydroaid, heating such solution to effect reaction between anyprecipitated basic lead compounds and the remaining iron in solution toform the insoluble iron precipitate and the soluble lead compound andfinally adding sutiicient sodium carbonate to precipitate the remainingsmall amount of iron as ferric hydroxid.

3. The process of purifying impure lead nitrate solution from relativelysmall amount of iron'in solution which consists in adding sullicientalkali precipitate to major portion of the iron as hydroztid andsubsequently adding suli'icient alkali to precipb tate the entireremaining portion of the iron.

In testimony whereof we alliir our signatures in presence of twowitnesses.

* SAMUEL TV. .lltDlillttfSGN.

GROVER C. liar-till.

Witnesses L. L "i VnsTrALL, WILLIAM H. Kara.

Ittlii Lilli

